Astronomy Ch.20 Mastering Astronomy

The disk component of a spiral galaxy includes which of the following parts? A. globular clusters B. bulge C. spiral arms D. halo E. all of the above

C. spiral arms

Why are Cepheid variables important? A. Cepheid variables are stars that vary in brightness because they harbor a black hole. B. Cepheids are a type of young galaxy that helps us understand how galaxies form. C. Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future. D. Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

D. Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

Following are a number of distinguishing characteristics of spiral and elliptical galaxies. Match each characteristic to the appropriate galaxy type. 1. Contain many bright, hot stars 2. Are more reddish in color 3. Are rare in central regions of the galaxy clusters 4. have significant ongoing star formation 5. contain primarily old, low-mass stars 6. have a flattened disk of stars 7. contain abundant clouds of cool gas and dust

SPIRAL : 6. have a flattened disk of stars 3. Are rare in central regions of the galaxy clusters 1. Contain many bright, hot stars 7. contain abundant clouds of cool gas and dust 4. have significant ongoing star formation ELIPTICAL : 2. Are more reddish in color 5. contain primarily old, low-mass stars

What is the most accurate way to determine the distance to a nearby star? A. stellar parallax B. radar ranging C. using Cepheid variables D. Hubble's law

A. stellar parallax

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies? A. There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy. B. From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy. C. Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way. D. He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy.

B. From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.

How did Edwin Hubble measure the distance to the Andromeda Galaxy? A. He measured its parallax. B. He applied the period-luminosity relation to Cepheid variables. C. He used white dwarf supernovae. D. He deduced it from its redshift.

B. He applied the period-luminosity relation to Cepheid variables.

Compared to spiral galaxies, elliptical galaxies are A. redder and flattened. B. redder and rounder. C. bluer and rounder. D. bluer and flattened. E. always much smaller.

B. redder and rounder.

White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which? A. White-dwarf supernovae are so bright that they can be detected even in very distant galaxies. B. White-dwarf supernovae are common enough that we detect several every year. C. White-dwarf supernovae occur only among young and extremely bright stars. D. All white-dwarf supernovae have similar light curves, which makes them easy to distinguish from massive-star supernovae. E. All white-dwarf supernovae involve the explosion of stars of nearly the same mass.

C. White-dwarf supernovae occur only among young and extremely bright stars.

What is a standard candle? A. a long, tapered candle that lights easily B. a class of objects in astronomy that all have exactly the same luminosity C. an object for which we are likely to know the true luminosity D. any star for which we know the exact apparent brightness E. an object for which we can easily measure the apparent brightness

C. an object for which we are likely to know the true luminosity

Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest? A. parallax, white-dwarf supernovae, Hubble's law B. parallax, Hubble's law, white-dwarf supernovae C. parallax, Cepheid variables, Hubble's law D. parallax, Hubble's law, Cepheid variables

C. parallax, Cepheid variables, Hubble's law

Which types of galaxies have a clearly defined halo component? A. lenticulars only B. ellipticals only C. irregulars only D. spirals only E. all but irregulars

E. all but irregulars

What makes white-dwarf supernovae good standard candles? A. They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. B. They should all have approximately the same luminosity. C. We have had several occur close to us in the Milky Way, so we have been able to determine their luminosities very accurately. D. They occur so frequently that we can use them to measure the distances to virtually all galaxies. E. both A and B

E. both A and B